The overall long-term objective of this Program Project is to identify novel dietary and hormonal determinants of breast colorectal and ovarian cancer risk in women, with the ultimate aim to find means for prevention and improved survival. The combination of questionnaire derived data with biomarkers, coupled with the long-follow-up, affords the opportunity to further understanding of the time course and mechanisms of cancer development. To achieve these objectives, we will relate a) prospectively collected data on diet, post-menopausal hormone use, smoking, and other behaviors; b) nutrient and hormone levels in prospectively collected blood; and c) genotyping information form archived DNA and tissue blocks; to incidence of breast colorectal, and ovarian cancer. This Program Project is based on the Nurses' Health Study cohort comprising 1212,700 women who were 30 to 55 years of age when enrolled in 1976. The Program Project serves as the central resource for the many related grants addressing incidence of cancer and other major chronic diseases that arise in this cohort of women. Project 1. Diet, exogenous hormones and breast cancer risk. Project 2. Diet, hormones and brisk of colorectal cancer. Project 3. Hormones, diet and risk of ovarian cancer. Project 4. Statistical innovations in risk modeling.